American businessman Jacob Holder met his Thai husband Surapong Koonpaew in 2021, got married in the United States two years later and then returned to Thailand, where they live and work.

This week, their union will be recognised under Thai law, after the country's marriage equality bill passed by parliament last year comes into force on Jan. 22, capping decades of efforts by activists.

Thailand will become the first country in Southeast Asia and third place in Asia to recognise marriages of same-sex couples.

But for couples like Holder and Surapong the new law, although historic and progressive, still leaves them with hurdles to building a legally recognised family.

Soon after their wedding, the couple had a son, Elijah Bprin Holder Koonpaew, born through legal surrogacy in Colombia since that option is not available to same-sex couples in Thailand.

Elijah Bprin has the names of both of his parents on a U.S. birth certificate, Jacob said, but the 18-month-old must live in Thailand on a tourist visa.

Elijah has no legal relationship with Surapong in Thailand due to the absence of a same-sex couple surrogacy law and the strict definition of a parent.

Thailand's traditional definition of a family - a father being a man and a mother a woman - remains in Thai legal codes, in spite of the passage of the marriage equality law.

"Legally, they have no connection," Jacob said of his son and his husband Surapong, a civil servant who also goes by the nickname Keng.

"If tomorrow, God forbid, something did happen to me, we have real concerns (about) what then happens between Keng and our son under the eyes of the Thai law."

The Thai health ministry is working on a draft bill to allow same-sex couple surrogacy, but it is unclear how long the process will take and whether it would be successful.

Thailand's new marriage equality bill will now allow same-sex couples to adopt a child.

But due to the legal definition of a parent, same-sex couple "qualification" as adoptive parents would, in practice, depend on official consideration, which experts say could lead to discrimination.